Motor torque control method, apparatus, and computer readable medium for air blower

ABSTRACT

A motor torque control method for an air blower may include: setting a phase current command value of a motor of the air blower based on a temperature of the motor, calculating a d-axis current command value other than zero in compliance with the set phase current command value, and outputting the calculated d-axis current command value.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of KoreanPatent Application Number 10-2014-0067873 filed on Jun. 3, 2014, theentire contents of which application are incorporated herein for allpurposes by this reference.

BACKGROUND

1. Technical Field

The present disclosure relates, in general, to a motor torque controlmethod for an air blower and, more particularly, to a motor torquecontrol method for an air blower, which can rapidly raise thetemperature of a fuel cell stack in a cold-start condition.

2. Description of the Related Art

As is understood in the art, a typical fuel cell vehicle includes a fuelcell stack in which a plurality of fuel cells used as a power source arestacked one on top of another, a fuel supply system for supplying a fuel(e.g., hydrogen or the like) to the fuel cell stack, an air supplysystem for supplying oxygen, which is an oxidant required forelectrochemical reactions, a water/heat management system forcontrolling the temperature of the fuel cell stack, etc. The fuel supplysystem decompresses compressed hydrogen in a hydrogen tank and suppliesdecompressed hydrogen to the fuel electrode (anode) of the stack. Theair supply system supplies external air, drawn in by operating an airblower, to the air electrode (cathode) of the stack.

When hydrogen is supplied to the anode of the stack and oxygen issupplied to the cathode, hydrogen ions are separated at the anode via acatalytic reaction. The separated hydrogen ions are transferred to anoxidation electrode, which is the cathode, through an electrolytemembrane. The hydrogen ions separated at the anode, electrons and oxygentogether cause an electrochemical reaction at the oxidation electrode,and thus, electrical energy can be obtained through such a reaction. Indetail, an electrochemical oxidation of hydrogen occurs at the anode,and an electrochemical reduction of oxygen occurs at the cathode. Due tothe movement of electrons generated in this procedure, electricity andheat are generated, and vapor or water is generated due to a chemicalaction in which hydrogen and oxygen combine.

A discharge device is provided to discharge by-products such as vapor,water and heat, which are produced when generating the electrical energyof the fuel cell stack, the unreacted hydrogen, oxygen, etc. Gases suchas vapor, hydrogen and oxygen are discharged to the atmosphere through adischarge path.

Components such as an air blower, a hydrogen recirculation blower, and awater pump for driving fuel cells, are connected to a main bus terminalto facilitate starting of the fuel cells. Various types of relays forfacilitating power disconnection and connection, as well as a diode forpreventing a reverse current from flowing into the fuel cell, may beconnected to the main bus terminal.

Air supplied through the air blower is humidified by a humidifier, andis then supplied to the cathode (air electrode) of the fuel cell stack.An exhaust gas from the cathode is transferred to the humidifier withthe exhaust gas humidified by internally generated water components, andmay be used to humidify dry air to be supplied to the cathode throughthe air blower. Such an air blower may include a motor, a magnetic rotorfor generating turning force (torque), a blade for drawing in air, andthe like.

Meanwhile, the motor included in the air blower may be a permanentmagnet synchronous motor. FIG. 1 is a graph showing a relationshipbetween a q-axis current command i_(q)* and a d-axis current commandi_(d)* in a permanent magnet synchronous motor control system.Typically, in compliance with a torque command from an upper-levelcontroller or an external system, a current command generator (notshown) generates a q-axis current command (e.g., torque split currentcommand) corresponding to the torque command, and generates a d-axiscurrent command (e.g., magnetic flux split current command), wherein thed-axis current command is set to ‘0’ in order to operate the motor atmaximum efficiency.

The current commands generated by the current command generator areoutput to a current controller (not shown), and the current controllergenerates d-axis and q-axis voltage commands. Thereafter, a 3-phasevoltage command is generated, and the motor is controlled via a pulsewidth modulation (PWM) procedure and a 3-phase current controlprocedure.

Meanwhile, when the fuel cell vehicle stops, an amount of watergenerated during driving remains in the fuel cell stack. Further, whenthe external temperature of the vehicle is very low, such remainingwater is condensed to cause a phase change to ice, and then a problemarises in that starting of the fuel cell vehicle is impossible. In orderto secure cold-startability in such a cold-start environment, a methodfor rapidly defrosting a coolant using a heater and a method ofinstalling a heater on an air supply system line and raising thetemperature of air may be utilized.

However, a method of installing a heater on a suction line between theair blower and the humidifier during cold-starting, or a method ofheating the fuel cell stack by circulating warm air discharged from thefuel cell stack through the inside of an enclosure that surrounds thefuel cell stack is problematic in that an additional heater must bemounted, and the structural change of the fuel cell stack is required,thus complicating the arrangement design of component parts andincreasing production costs. In addition, there is a problem in thatexcessive time is required to operate a heater and raise the temperatureof the fuel cell stack to a suitable level.

SUMMARY

Accordingly, the present disclosure has been made keeping in mind theabove problems occurring in the related art, and an object of thepresent disclosure is to provide a motor torque control method for anair blower, which can rapidly raise the temperature of a fuel cell stackby operating the motor of the air blower of a fuel cell vehicle at lowefficiency.

In order to accomplish the above object, the present disclosure providesa motor torque control method for an air blower, including setting aphase current command value of a motor of the air blower based on atemperature of the motor; calculating a d-axis current command valueother than zero in compliance with the set phase current command value;and outputting the calculated d-axis current command value.

The d-axis current command value may be calculated using the set phasecurrent command value and a q-axis current command value determined incompliance with an input speed command value.

A value at which the phase current command value is set may decrease asthe temperature of the motor of the air blower increases.

The motor torque control method may further include determining whethera present condition is a cold-start condition in which an externaltemperature of a fuel cell vehicle is less than or equal to a presettemperature, wherein the phase current command value of the motor may beset based on the temperature of the motor only when it is determinedthat the present condition is a cold-start condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich: FIG. 1 is a graph showing a relationship between a q-axis currentcommand i_(q)* and a d-axis current command i_(d)* in a conventionalpermanent magnet synchronous motor control system;

FIG. 2 is a graph showing d-axis and q-axis current commands in thelow-efficiency operation of the motor of an air blower according toembodiments of the present disclosure; and

FIG. 3 is a flowchart showing a motor torque control method for an airblower according to embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Specific structural or functional descriptions related to embodimentsaccording to the present disclosure and disclosed in the presentspecification or application are merely illustrated to describeembodiments of the present disclosure, and the embodiments of thepresent disclosure may be implemented in various forms and should not beinterpreted as being limited to the embodiments described herein. Theembodiments according to the present disclosure may be modified invarious manners and may have various forms, so that specific embodimentsare intended to be illustrated in the drawings and described in detailin the present specification or application. However, it should beunderstood that those embodiments are not intended to limit theembodiments based on the concept of the present invention to specificdisclosure forms and they include all changes, equivalents ormodifications included in the spirit and scope of the presentdisclosure.

The terms such as “first” and “second” may be used to describe variouscomponents, but those components should not be limited by the terms. Theterms are merely used to distinguish one component from othercomponents, and a first component may be designated as a secondcomponent and a second component may be designated as a first componentin the similar manner, without departing from the scope based on theconcept of the present disclosure.

Throughout the entire specification, it should be understood that arepresentation indicating that a first component is “connected” or“coupled” to a second component may include the case where the firstcomponent is connected or coupled to the second component with someother component interposed therebetween, as well as the case where thefirst component is “directly connected” or “directly coupled” to thesecond component. In contrast, it should be understood that arepresentation indicating that a first component is “directly connected”or “directly coupled” to a second component means that no component isinterposed between the first and second components.

Other representations describing relationships among components, thatis, “between” and “directly between” or “adjacent to,” and “directlyadjacent to,” should be interpreted in similar manners.

The terms used in the present specification are merely used to describespecific embodiments and are not intended to limit the presentdisclosure. A singular expression includes a plural expression unless adescription to the contrary is specifically pointed out in context. Inthe present specification, it should be understood that the terms suchas “include” or “have” are merely intended to indicate that features,numbers, steps, operations, components, parts, or combinations thereofare present, and are not intended to exclude a possibility that one ormore other features, numbers, steps, operations, components, parts, orcombinations thereof will be present or added.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

Unless differently defined, all terms used here including technical orscientific terms have the same meanings as the terms generallyunderstood by those skilled in the art to which the present inventionpertains. The terms identical to those defined in generally useddictionaries should be interpreted as having meanings identical tocontextual meanings of the related art, and are not interpreted as beingideal or excessively formal meanings unless they are definitely definedin the present specification.

Additionally, it is understood that the below methods may be executed byat least one controller. The term “controller” refers to a hardwaredevice that includes a memory and a processor. The memory is configuredto store program instructions, and the processor is configured toexecute the program instructions to perform one or more processes whichare described further below. Moreover, it is understood that the belowmethods may be executed by an apparatus comprising the controller,whereby the apparatus is known in the art to be suitable for performinga motor torque control method for an air blower, which can rapidly raisethe temperature of a fuel cell stack in a cold-start condition.

Furthermore, the controller of the present disclosure may be embodied asnon-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor,controller or the like. Examples of the computer readable mediumsinclude, but are not limited to, ROM, RAM, compact disc (CD)-ROMs,magnetic tapes, floppy disks, flash drives, smart cards and optical datastorage devices. The computer readable recording medium can also bedistributed in network coupled computer systems so that the computerreadable media is stored and executed in a distributed fashion, e.g., bya telematics server or a Controller Area Network (CAN).

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the attached drawings. The same referencenumerals are used throughout the different drawings to designate thesame or similar components.

FIG. 2 is a graph showing d-axis and q-axis current commands in thelow-efficiency operation of the motor of an air blower according toembodiments of the present disclosure. Referring to FIG. 2, it can beseen that a d-axis current command i_(d)* is not zero as in the case ofFIG. 1. When the d-axis current command is not zero, it means that theefficiency of a current command value for the required torque is not100%. The motor acts as a single additional load because the d-axiscurrent command is not operated at maximum efficiency when the motor ofthe air blower is operated. As the motor is not operated at the maximumefficiency, that is, as much power is used for the same output, thermalenergy is generated, and the temperature of the fuel cell stack may beraised via the thermal energy. Further, since much power is used, theconsumption of electric power generated by the fuel cell stack isfurther increased, so that the required output of the fuel cell stack isincreased, thus further activating an electrochemical reaction in thefuel cell stack. As a result, a heating value is increased, and thus thetemperature of the fuel cell stack can be rapidly raised.

Further, in the conditions in which low-efficiency operation of themotor, other than maximum-efficiency operation, is required, as well asa cold-start condition, for example, in the flooded state of the fuelcell stack or in a case where the high voltage battery is in afully-charged state during driving on a long downhill road, the motor ofthe air blower may be operated as an additional load.

FIG. 3 is a flowchart showing a motor torque control method for an airblower according to embodiments of the present disclosure.

Referring to FIG. 3, it is determined whether a present condition is acold-start condition in which the external temperature of the fuel cellvehicle is equal to or less than a preset temperature at step S301. Ifit is determined that the present condition is a cold-start condition,the phase current command value I_(s) of the motor of the air blower isset based on the temperature of the motor at step S303. Such a phasecurrent command value I_(s) may be determined based on the temperatureof the motor and the current capacity of the Insulated Gate BipolarTransistor (IGBT) of an inverter.

If the phase current command value I_(s) of the motor of the air bloweris set based on the temperature of the motor, a d-axis current commandvalue i_(d)* other than zero is calculated in compliance with the setphase current command value at step S305. Then, the calculated d-axiscurrent command value may be output at step S309. The d-axis currentcommand value is calculated using the set phase current command valueI_(s) and a q-axis current command value i_(q)* determined in compliancewith an input speed command value. The phase current command value maybe set to a smaller value as the temperature of the motor of the airblower increases, whereas it may be set to a larger value as thetemperature of the motor of the air blower decreases.

A relationship between the set phase current command value, the d-axiscurrent command value and the q-axis current command value may berepresented by the following Equation (1):

i _(d) *=I _(s) ² −i _(q)*²  (1)

That is, as the value of I_(s) is set to a larger value, the d-axiscurrent command value is increased. Further, as the temperature of themotor is lower, the d-axis current command value is increased.

In conditions other than the cold-start condition, the d-axis currentcommand value is set to zero as in existing schemes, and the q-axiscurrent command value may be the output of a speed controller at stepS307. The determined d-axis current command value and q-axis currentcommand value are output to a current controller (not shown).

In accordance with the motor torque control method for an air bloweraccording to embodiments of the present disclosure, there is anadvantage in that the current command value of the air blower isadjusted to operate the motor at low efficiency, so that, as requiredpower is increased, an electrochemical reaction in a fuel cell stack canbe increased, and a heating value can also be increased, thus rapidlyraising the temperature of the fuel cell stack. Further, the motor ofthe air blower is operated as an additional load, thus preventing theair blower from being operated at an open circuit voltage and preventingthe fuel cell stack from being flooded. Furthermore, when a high voltagebattery is in a fully-charged state, regenerative braking energy can beconsumed by the motor of the air blower.

Although the embodiments of the present disclosure have been describedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the disclosure as disclosed inthe accompanying claims. Therefore, the technical scope of the presentdisclosure should be defined by the technical spirit and scope of theaccompanying claims.

What is claimed is:
 1. A motor torque control method for an air blower,comprising: setting, by a controller, a phase current command value of amotor of the air blower based on a temperature of the motor;calculating, by the controller, a d-axis current command value otherthan zero in compliance with the set phase current command value; andoutputting, by the controller, the calculated d-axis current commandvalue.
 2. The motor torque control method of claim 1, wherein the d-axiscurrent command value is calculated using the set phase current commandvalue and a q-axis current command value determined in compliance withan input speed command value.
 3. The motor torque control method ofclaim 1, wherein a value at which the phase current command value is setdecreases as the temperature of the motor increases.
 4. The motor torquecontrol method of claim 1, further comprising determining, by thecontroller, whether a present condition is a cold-start condition inwhich an external temperature of a fuel cell vehicle is less than orequal to a preset temperature, wherein the phase current command valueof the motor is set based on the temperature of the motor only when itis determined that the present condition is a cold-start condition.
 5. Amotor torque control apparatus for an air blower, comprising: a memoryconfigured to store program instructions; and a processor configured toexecute the program instructions so as to perform a process including:setting a phase current command value of a motor of the air blower basedon a temperature of the motor, calculating a d-axis current commandvalue other than zero in compliance with the set phase current commandvalue, and outputting the calculated d-axis current command value.
 6. Anon-transitory computer readable medium containing program instructionsfor performing a motor torque control method for an air blower, executedby a processor or controller, the computer readable medium comprising:program instructions that set a phase current command value of a motorof the air blower based on a temperature of the motor; programinstructions that calculate a d-axis current command value other thanzero in compliance with the set phase current command value; and programinstructions that output the calculated d-axis current command value.